I would love to harvest tons of currants especially the black ones! But unfortunately, our harvest is small since we have this pesky currant borer around here. I tried to prune all affected stems out cutting them in tiny pieces, I tried to plant around 100 garlic chives around the currant bushes because that is what google said - it did not help. Does anyone has a solution to that borer problem? Everyone has it around here.
Don't have experience with this, but they must have some natural predator, and if you can find some way to leave some around long enough, that predator will show up--that's what Paul just said in the podcast I'm listening to (review of Gaia's Garden chapter 7, podcast 075.)
Diatomaceous earth could help in the immediate and be safe for the ecosystem...but even that will probably kill some beneficial bugs as well as the ones you don't want.
Do you have a lot of currants all growing together? could you let some diversity grow in in the middle of the area, to make a bit of an edge/border through the middle of that section?
From my web search, it looks like current conventional opinion is that there are few natural predators...so if you do observe something eating them you're doing some new research.
Some other things you might try if you have them:
bird bath (to attract birds that might like to eat them?)
This information brought to you by my butt. May not be true in any way.
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Something I just noticed in your post, when you say you pruned out the affected branches and cut them into tiny pieces, is that the branches or the insects you cut into pieces? If the branches, what did you do with them afterwards?